2,5-Dipicryl thiophenes

ABSTRACT

Heat resistant explosives of the formula   WHEREIN R1 and R2 are selected from the group consisting of H and NO2. Compounds wherein R1 and R2 are prepared by contacting a picryl halide with a thiophene of the formula   WHEREIN X is a halogen. When either or both of R1 and R2 are NO2, nitration of 2,5-dipicryl thiophene can be used to prepare the desired compounds.

limited States Pate Sitzmann et al.

[111 wzmso 1 Dec. 2, 1975 1 i 2,5-DlPlCRYL THIOPHENES [75] Inventors: Michael E. Sitzmann, Chevy Chase, Md.; Joseph C. Dacons, Washington, DC.

[73] Assignee: The United States of America as represented by the Secretary of the Navy, Washington, DC.

221 Filed: Oct. 4, 1972 211 App1.No.: 298,089

[52] U.S. Cl. 260/329 R; 149/105 [51] int. Cl. C07D 333/12 [58] Field of Search 149/105; 260/329 R [56] References Cited OTHER PUBLICATIONS Babasinan, J. Am. Chem. Soc., Vol. 50. pp. 2748 to 2753, (1928). l-lartough, Thiophene and Its Derivatives, Interscience Publishers, Inc., N.Y., 1952, p: 476.

Primary Examiner-Leland A. Sebastian Attorney, Agent, or FirmR. S. Sciascia; J. A. Cooke [57] ABSTRACT Heat resistant explosives of the formula wherein R, and R are selected from the group consisting of H and N0 Compounds wherein R and R are prepared by contacting a picryl halide with a thiophene of the formula wherein X is a halogen. When either or both of R and R are N0 nitration of 2,5-dipicryl thiophene can be used to prepare the desired compounds.

4 Claims, No Drawings 2,5-DIPICRYL THIOPHENES BACKGROUND OF THE INVENTION This invention generally relates to explosives and more particularly to explosives with excellent heat stability.

Use of explosives in many different types of devices is widely known in the prior art. However, despite the huge number of explosives that are known there are relatively few that can withstand high temperatures in the range of 230260C or above without substantial deterioration. Since explosives in many specialized uses are subjected to temperatures of about 230C or higher there has been a constant search for explosive materials which will not deteriorate substantially due to high temperatures.

SUMMARY OF THE INVENTION Accordingly, one object of this invention is to provide new chemical compounds.

Another object of this invention is to provide chemical compounds that can be used as explosives.

A further object of this invention is to provide explosive compounds which are capable of withstanding temperatures in the range of 230-260C and above without substantial deterioration.

A still further object of this invention is to provide explosive compounds which can be used in environments wherein high temperatures are a problem (i.e., where aerodynamic heating is a problem).

Yet another object of this invention is to provide explosive compounds which can be used in mild detonating cord and flexible linear shaped charges.

These and other objects of this invention are accomplished by providing chemical compounds of the formula wherein R and R are selected from the group consisting of H and N which are prepared by reacting picryl bromide or any picryl halide, with a thiophene of the formula wherein X is halogen or by first reacting picryl bromide with 2,5-dihalothiophene to form the 2,5-dipicrylthiophene and then nitrating using standard nitration conditions.

DESCRIPTION OF THE PREFERRED EMBODIMENT Compounds of the formula wherein R and R are H or N0 are prepared in one of two ways. One may prepare them by contacting the appropriate thiophene of the formula wherein X is halogen with picryl bromide under the typical Ullman biaryl synthesis. Compounds wherein one or both of R and R are N0 can also be prepared by nitration of 2,5-dipicrylthiophene which is formed using the Ullman biaryl synthesis.

With the Ullman synthesis the thiophene is dissolved in a solvent such as nitrobenzene and copper bronze is added. The picryl bromide is then added dropwise to the above solution over a period of about one-half hour and the temperature is maintained at about 150C. Following this the solution are purified using typical purification techniques.

The thiophenes wherein one or both of R and R are N0 can also be prepared by direct nitration of 2,5-dipicrylthiophene. When one of R and R is N0 nitric acid at 45C for about 10 minutes gives almost quantitative yields. When both R and R are N0 nitration by using 90% nitric acid and 30% oleum at 60C for about 2 hours is preferred.

The general nature of the invention having been set forth, the following examples are presented as specific illustrations thereof. It will be understood that the invention is not limited to these specific examples but is susceptible to various modifications that will be recognized by one of ordinary skill in the art.

EXAMPLE 1 PICRYL BROMIDE An amount of 355 g (3.5 moles) of reagent grade potassium nitrate was dissolved in 800 ml of 30% oleum in a 2,000 ml 3-neck round bottom flask fitted with a mechanical stirrer and a thermometer. During the addition of the potassium nitrate, the mixture was cooled and stirred on an ice bath, the temperature being kept below 60C. When the addition was complete, the mixture was cooled to 30C and 79 g (0.5 moles) of bromobenzene was added at such a rate as to keep the temperature below 50C. The ice bath was then replaced by an oil bath and the reaction mixture was heated to approximately C for four hours. After cooling, the mixture was drowned in crushed ice, the product was collected by filtration using a sintered glass funnel and thoroughly washed with water. After drying in a warm oven, it was dissolved in 100 ml of acetone, 300 ml of methanol was added and the solution was cooled in the freeze compartment of the refrigerator. On filtration, 83.7 g of pale yellow crystalline picryl bromide, mp l20122C (lit. l223C) was recovered. The filtrate was concentrated to about ml by boiling on the steam bath and again cooled in the freeze compartment. The second crop weighed 28.0 g and melted over the range 111118C. On recrystallization from acetone-ethanol, an additional 21.0 g of crystalline product, mp 120122C was obtained to give a total yield melting at this temperature of 104.7 g, 71.6%. Samples melting at 122123C were obtained by one additional recrystallization from acetone-methanol.

EXAMPLE 2 2,5-DIPlCRYLTl-IIOPHENE A stirred mixture of 19.4 g (0.08 moles) of 2,5- dibromothiophene and 45.7 g (0.72 moles) of copper bronze in 80 ml of dry nitrobenzene was rapidly heated to 145C in a 500 ml 3-neck round bottom flask equipped with a mechanical stirrer, a thermometer and an addition funnel. Approximately one-half of a solution containing 58.4 g (0.20 moles) of picryl bromide in 150 ml of dry nitrobenzene was added over a period of minutes with the temperature at 145150C. The remaining half of the solution was added over a period of 25 minutes. The dark reaction mixture was then allowed to cool to 100C and was poured into 300 ml of toluene. The mixture was cooled to 10C in an ice bath and filtered. The insoluble residue was washed with methanol then stirred in 800 ml of 20 percent hydrochloric acid at 6070C for minutes. The acidinsoluble residue was removed by filtration and was washed on the funnel with dilute hydrochloric acid, water and finally methanol. The product (37.6 g), which contained unreacted copper, was stirred with 300 ml of dimethylsulfoxide at 100C and filtered. The residue on the funnel was washed with an additional 50 ml of hot dimethylsulfoxide and the dark filtrate was treated with g of activated charcoal at 100C. The charcoal was removed by filtration and the filtrate was added slowly with stirring to 700 ml of methanol causing the product to precipitate. The suspension was cooled to 5C on an ice bath and filtered. The bright yellow product was washed with methanol and dried at 120C under vacuum for one hour to give 31.3 g (76.8%) of 2,5-dipicrylthiophene, m.p. 359360C (d) (darkens above 300C). This product was dissolved in 500 ml of nitrobenzene at 165C and recrystallized by slowly cooling to room temperature. On filtering, washing with 150 ml of methanol and drying under vacuum at 130C for 2 hours, the product was 29.1 g of golden yellow crystals, m.p. 359360C (d). On adding an additional 250 ml of methanol to the filtrate and cooling in an ice bath, an additional 1.3 g of product having the same melting point was recovered. The total yield was 30.4 g (75.1%). Both crops were chromatographically pure and darkened slowly on heating above 300C.

EXAMPLE 3 2,5-DIPICRYL-3-NITROTHIOPHENE To a stirred volume of 250 ml of 90 percent nitric acid was added 25.3 g (0.05 moles) of 2,5dipicrylthiophene. The temperature was then raised to 45C to effect complete solution of the solid. The solution was stirred approximately two minutes and poured into one liter of ice water with vigorous stirring. The product was removed by filtration, thoroughly washed with water and, since the water-wet material was very difficult to handle, it was thoroughly washed with methanol on the funnel. After drying under vacuum at 120C for 2 hours, the yield of crude 2,5-dipicryl-3- nitrothiophene was 27.1 g (98.4%), m.p. 285286C (d). Thin-layer chromatography indicated that the product was free of both the starting material and the dinitro derivative. The product was dissolved in 350 ml of hot acetone, the solution was treated with a small amount of activated charcoal and filtered. The bright yellow filtrate was concentrated by distillation until precipitation occurred (volume was about ml). Methanol was slowly added with continued distillation until the temperature of the distillate reached 63C and the volume was about 200 ml. The mixture was cooled in an ice bath, filtered and washed with methanol to give 26.3 g (95.5%) of bright yellow crystals, m.p. 287-288C (d).

EXAMPLE 4 2,5-DIPICRYL-3,4-DINITROTHIOPHENE BY" ULLMANN BIARYL SYNTHESIS To a slurry of 6.4 g (0.1 moles) of copper bronze and 40 ml of nitrobenzene stirred at l85190C was added a solution containing 3.32 g (0.01 moles) of 2,5- dibromo-3,4-dinitrothiophene, prepared according to Monzingo, et al. and 9.9 g (0.04 moles) of picryl chloride in 40 ml of nitrobenzene dropwise over a period of five minutes. Heating at 185190C was continued for ten minutes after the addition was complete. The dark mixture was cooled to C, filtered and the filtrate was added to 150 ml of benzene. After cooling on an ice bath and filtering, a precipitate weighing 5.6 g was recovered. Thin-layer chromatography using benzeneacetone 85:15 as the developer showed this product to be a mixture, one component of which was 2,2',4,4,6,- 6'-hexanitrobiphenyl. The solid was dissolved in a minimal amount of acetone; the solution was treated with activated charcoal and filtered. Acetone was removed by distillation while benzene was slowly added causing the precipitation of a solid product. This was continued until the temperature of the distillate was 70C. After removal from the hot solution by filtration, the product weighed 2.75 g and melted at 295298C with decomposition. Recrystallization by dissolving in a minimal amount of hot acetonitrile, adding benzene to effect precipitation and cooling in ice gave a yield of 2.1 g (35%) of bright yellow crystals, m.p. 305306C ((1). After drying under vacuum at C for 1 hour, the n.m.r. spectrum showed singlets at 7.34 and 9.31 ppm. The latter was reasonable for the four equivalent protons of 2,5-dipicryl-3,4-dinitrothiophene, but the singlet at 7.34 ppm was thought to be due to the presence of benzene in the sample, probably as benzene of solvation. Vapor phase chromatographic analysis showed this to be the case. An analytical sample was prepared by drying this material an additional 6 hours under vacuum at 130C.

EXAMPLE 5 2,5-DlPlCRYL-3,4-DINITROTHIOPHENE BY NITRATION Two grams of 2,5-dipicrylthiophene were stirred into 30 ml of 90 percent nitric acid at 60C. Thin-layer chromatography indicated that a small sample removed 3 minutes after solution was complete contained only 2,5-dipicryl-3-nitrothiphene. The nitric acid solution was cooled to 15C and 10 ml 30 percent oleum was slowly added causing a rise in temperature to 50C. The reaction mixture was then heated to 60C for one hour and forty-five minutes and poured onto an excess of crushed ice. The aqueous mixture was filtered to give 2.2 g of a bright yellow solid, mp. 298300C (d). Crystallization from acetonitrile-benzene yielded 2.15 g of bright yellow crystals which lost benzene of solvation after drying two hours at 140C (see preparation of this product by the Ullmann biaryl synthesis). The dried product weighed 1.90 g (79.1%) and melted at 303304C with decomposition. An additional recrystallization from acetonitrile-benzene gave 1.8g of pure 2,5-dipicryl-3,4-dinitr0thiophene, m.p. 304305C after drying under vacuum at 140C. This product was identical (TLC) to that prepared by the Ullmann biaryl synthesis.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described herein.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. Compounds of the formula 

1. COMPOUND OF THE FORMULA
 2. The compound of claim 1 wherein both R1 and R2 are H.
 3. The compound of claim 1 wherein both R1 and R2 are NO2.
 4. The compound of claim 1 wherein R1 is H and R2 is NO2. 